Prioritised off-grid power

Wondering if anyone has considered, designed or built an off-grid electric system which has separate storage for essential and nonessential uses.
The idea being to maximise the uptime of essential loads. These might include refrigerator, freezer, and water filtration (if UV is used). These would have a dedicated battery bank designed to cope with 3-4 days of no generation. It would provide protection against stupid mistakes such as leaving lights on
Nonessential loads is basically everything else: Lights, phone & laptop charging, small kitchen appliances, electric blankets (yes, we've found we have sufficient power for 30-minute bed warm-up, loving it!) entertainment etc.
The essentials battery bank would have first priority for being charged. It would also be able to draw from the nonessentials battery bank (possibly via a step-up if the NE voltage is lower than the E, obviously limited to cut off at minimum recommended voltage (10.5V / 21V)
Could this be managed with the likes of a Raspberry Pi and some relays?
Also important is an inverter which can automatically turn itself on again if voltage has recovered after a low-voltage trip - does such a thing exist?

I'm not sure this would be a good strategy in terms of different battery banks. You don't ever want to empty a battery bank, and you want to get it back to fully charged as soon as possible to maintain battery health. If you accidentally leave an appliance on and empty your bank you are much better off in terms of money and fossil fuel use (batteries pollute too!) to fire up a generator and charge the bank back up. Much of solar/wind design revolves around the charge time for the battery bank. Keep your bank properly charged and it will last for a long time. Lax on that end and it's easy to ruin batteries forever.

However I think you can accomplish your goals in other ways. You can monitor your single battery bank and automatically switch off appliances once you hit a certain threshold. In fact that would be super clever! You could even tie it into your charge controller and turn on extra appliances when you've filled your bank and are in surplus. I know a few people who have similar setups to various degrees (usually turning on extra pond pumps or ice makers) — but theirs are all manual. I'm hoping myself to do all kinds of clever stuff with rpi's once I get my setup solid. But I also know I have a tendency to dream a more time-filled life than I live.

Do you have a setup you can experiment with? I'd love to follow along with experiments along these lines.

Hey Richard,

I have designed such a system but not really implemented it.  Most of my system was built out of necessity and as I had funds to build it.  I do diversify my system in the sense that I use a separate system for a shed, a separate system for my chicken houses, etc and of course my main focus is on my house which has it's own system.  I plan on building a wood working shop and it will have its own solar system for it as well.

We run appliances and have refrigeration and a freezer.  We have run out of battery storage before (due to AC unit in battery house not being on timer to turn off at night) and our inverter does automatically turn back on.  We have an AIMS Power 3000 Watt 24V Pure Sine Inverter Charger w/9000W Surge. It works well for our needs.  We have to pay attention to power consumption but the system provides our needs.  

We charge phones, multiple laptops, run TVs, Surround Home Theatre / Receiver, computer monitors, coffee grinders, blenders, mixers, shallow well pump, tankless water heater, samsung propane stove and oven (not efficient! The oven uses 500w), Fridgidaire Energy Star fridge (800w per day), egg incubators, lights throughout the house, air compressor, power tools, fans.  We run three fans a night, plus we have a 60w whole house fan, and Xbox regularly (I like smashing kids at NBA), and more I suppose.

We are forecasted for several days of overcast and we just don't use the TV, Xbox, electric eating oven, and etc until it passes.  

We plan on another battery bank and 900w array to run a chest freeze mid fall that will probably run on its own circuit to the house.

Add:  I have some plans in mind to use arduino to wirelessly communicate with my battery house to my house to control the system.  Maybe sometime in the future I will have time but it is not necessary now.

How often per year do you see this 'bad situation' happening.
If it is just once day per month a auto-star generator sound like a better option.

For me accidentally leaving the fridge(2000w) or freezer(2000) open or water/leak is much more likely to happen and also are a much bigger energy user than my 100Watt 55inch TV, 30watt laptop, 9w light bulb, My other big energy users microwave/toaster have a timer, even my blender would burnout after 30minutes so it effectively have a timer.

Now for emergency situation, I don't mind rebuying the food in the fridge, in fact I hardly use it, the freezer food would be alot harder to buy back, but really my biggest worry would be getting sick from dirty water or dieing from dehydration due to no water for 3+ days.  For that some kind of redundancy/failover sounds like a good idea (boiling the gallon or so of drinking water)

Hey Bengi what kind of TV do you have?  Mine draws way more and it is close to the end of days so I would like to get another.

As for me water is not a problem as we catch on everything: sheds, house, chicken coop, etc. We we can transport water to house fro jugs/buckets when the need arises and it does arise from time to time.

Here is a huge list
Low Power TV

Computer/small tv/tablet
https://www.amazon.com/Acer-Desktop-Pentium-Windows-AZ3-700-UR12/dp/B076H5X39R/ref=sr_1_2?s=electronics&ie=UTF8&qid=1533708554&sr=1-2&keywords=acer+aspire+az3-700&dpID=41FLiSPibjL&preST=_SX300_QL70_&dpSrc=srch

I should add some background info: We've been off-gridding for six years, but in a house we don't own. We are now planning our own build nearby.
Existing system is relatively small, solar plus hydro, 450 AH storage, with both panels and batteries renewed in the time we've been there. We have a Gram fridge (6 efficiency stars) but not enough power for the matching freezer, which lives in town. We live in temperate rainforest, so water is not a problem and is all gravity fed. But we can go for a week without a sunny day in winter, and the water feed can be knocked out by flooding.

In our new build we will have much more storage, and probably a solar wind combo now that there are good VAWTs available from China. (Getting a 50mm water feed across the road will not be cheap). We will probably run 24v generation and storage rather than 12V

It is mostly events while we are not at home that we are concerned about.

Now it all makes sense.

I like the idea of having one battery bank but with two different load branches.

One set of wires that is direct and another with a voltage controller. So once the voltage get "low"but not empty it turns of the inverter/etc branch.

Here is a low voltage cutoff device (11.5V,) http://www.evwest.com/catalog/product_info.php?products_id=295
'

Solar Electric Setup
$1000 PV panels 5x 275W about $200/each
PV support made of 2x4 just $70[
Wires and DC breakers about $100
$350 Charge Conroller SBMS100 4.5kW
$1000 Inverter 4kW
$1500 Lithium Battery 5.3kWHr or $2000
$1000 Backup Generator

I think it's better to prioritize loads rather than having multiple systems.  One battery bank works better than splitting it into two banks.

It's better to allow certain loads to run when the battery is charged above a given level.  Possibly add some predictive capabilities to estimate solar input based on weather predictions, etc.

I've been running a data collection system that measures energy use and solar production.  I have different loads classified as essential, useful, desired, and optional.  Essential loads are fridge, freezer, HVAC, home control servers, etc.  Useful loads, water heater, coffee maker, small kitchen appliances,  lights, etc. Desired: entertainment systems, laptops, etc.  Optional loads can be time shifted to when the battery bank is full but solar power is available: charging my EVs, running the dryer, etc.  I already control the water heater  so that it runs during the day and not at night.  Some of my loads are already controlled by the home control system; for example the water heater & climate control; eventually all of the optional and 'desired' loads will be controlled.
This all goes into a calculation that is estimating what size battery bank I'll need to provide essential and useful loads >99% of the time.   I've been running the calculations for a little over a year now, so far it looks like a 30kwh bank is the smallest I can get away with
For those rare occasions when the house battery ends up depleted, I could use the EV's batteries to run essential loads

I'm guessing that a lot of people that run off-gid systems do all of the above manually.

Kyle Neath wrote:I'm hoping myself to do all kinds of clever stuff with rpi's once I get my setup solid. But I also know I have a tendency to dream a more time-filled life than I live..

I'm building a system like that.  But with only one Pi, the master controller.  Individual loads are controlled by Arduino's.  You can run several dozen Arduino's on less power than 1 Raspberry Pi.
The system I'm working on uses Cat-5 cable to distribute power to the Arduino's and provide a 'network' using the built in Uarts on the Arduno's.

FWIW  a raspberry Pi 3 draws between 1.5 and 5 watts.  That can add up to 100 watt hours per day, per Pi.  If you used 10, that could be a killawatt hour per day just to power the Pi's.  
Depending on which Arduino you select, the stock models can use as little as 0.015 watts.  With some hardware mods and the proper code, you can run an Arduino off a coin cell battery for a year.

I currently have one Arduino that is measuring my household water consumption, inside temperature and humidity, attic temperature and humidity, the temp and humidity in in the server room, and it controls my evapaorative cooler based on calculations it runs on inside temp and humidity vs outside temp and humidity, and I'm only using about 1/4 of the available memory.  Some people even run webservers on them.

Peter: I've actually been playing a lot with ESP8266 and various ESP8266-based devices for this stuff. Figured raspberry pi's were a bit more known to most folks :)  In particular I have a bunch of ESP8266-based 'smart switches' (both plug models and raw wire models) that also monitor energy usage. This stuff is getting close to really accessible, but it sure does feel like you still need to be an expert in soldering and electronics to get anywhere right now.

It seems your idea of off -grid is different to mine.
When I think off grid I think of using peer so life is comfortable, but efficient.
Some of the items you list as essential surprise me.

For me lights and water pump are critical.

I dont use a fridge in winter, in summer its never an issue
Solar electric Hot water ?? in winter
it may be impossible and in summer solar hot water is perfect, I have LPG back up in winter or a water jacket on my wood heater.

Winter of course is the worst time in some climates for solar power, but using solar power to heat anything, in Australia, is considered madness, unless its over flow power from
collectors on Grid connected systems with low payback from the utilities supplier.

John C Daley wrote:
For me lights and water pump are critical.

I dont use a fridge in winter, in summer its never an issue
Solar electric Hot water ?? in winter

Lights are nice, but not essential.  We have battery powered lights for worse case situations.

We have a heat pump water heater, it only uses about 1kwh a day, give or take, and spits out cold air which can be useful during the summer, during the winter I duct the cold air outside and draw in replacement air from the attic(which can reach 90F during the winter).
I have a few friends with solar water heaters.  There are usually a couple weeks during the winter when they don't work at all, and even when they do work, they use 500-700 watts a day running the pumps, etc.  That's not that much less than my heat-pump water heater and mine works year-round.

Winter of course is the worst time in some climates for solar power, but using solar power to heat anything, in Australia, is considered madness, unless its over flow power from
collectors on Grid connected systems with low payback from the utilities supplier.

Propane costs money, sunshine is free.  Solar panels are dirt cheap right now.
Where I live we get as much energy from my solar array in February as we do in July,

As I said, the big loads (dryer/oven/Charging EVs) we can wait until the batteries are nearly full.  Since I've been monitoring energy flow, we've only had one occasion where we would have to wait more than 3-4 days...assuming a 30kwh pack and a 4.8kwh array.

I don't have anything close to a traditional battery bank. Almost all of my electrical use, involves tools. I have several Milwaukee, Makita, Stihl and Ego tools. These things aren't meant to run refrigeration, but they can do almost everything else listed.

Of course they can do all of the things that the tools are meant to do. I use them to build and demolish things, to cut trees and trim hedges.

I don't remember how much water my cordless Milwaukee pump moves. I think it was about 200 gallons on a charge.

I have a radio that works for several days on a large Makita battery. My largest Milwaukee battery could operate a cell phone for weeks with a simple adapter that's available for $18. Laptops can run from these same adapters. I have 4000 lumens of light available, should I ever require that much. I usually use about 500 lumens at once and one battery does me for several evenings. This isn't enough power to run a house in any sort of traditional manner, but it is vastly better than nothing. I show up at job sites that have no power, I work there all day and I sleep there. At night the radio and light are usually the only things used.

A good set of cordless tools would effectively work as a secondary battery bank. If you think you're getting close on the man bank, limit your entertainment and communication to whatever power these devices can give. I have a small movie player that draws 20 watts on average. Using the adapter, many movies could be watched using one of my Milwaukee batteries.

They sell a jacket that is basically an electric blanket. I met a welder who uses one of these jackets, because he doesn't want to be dressed really heavily when getting into tight spaces. A mid size battery does him for more than a day. If I see one going cheaply on the used market, I will pick it up. I sometimes find myself working on a building that isn't comfortable to live in. I sleep in the car. These jackets can also be plugged into a car's 12-volt system.

In this photo, I'm using one 1500 Lumen light, made by Milwaukee. It goes for 4 and 1/2 hours on a 5 amp hour battery. It's Illuminating a kitchen that's about 300 square feet. I usually use it on the half power setting so that it works for 9 hours.

Its fascinating to be aware you get heaps of solar in winter, my skies can be overcast for 3-4days, long enough to cause battery issues for me. But in other parts of the country grey skies are not a problem.

I am going on my third year in south central Missouri and I have seen 7-10 consecutive days  of overcast.  Its a concern for me preparing now to go into the coming winter and for that we plan on adding an additional array and addition battery bank to run parallel to our existing one in hope that we can scoot through this next winter.

Peter how do you separate those different prioritized loads?  How are you switching them on and off?

I have moved my priority loads over onto a new breaker panel in the garage.  That panel has a manual transfer switch, so I can switch it over to a generator or inverter running off the Chevy Volt, etc.
This is from the power monitoring system on the garage panel:


The mini-split heat-pump has a Wifi interface for controlling it,the Evap Cooler and Solar heater are controlled by an Arduino, the heat-pump water heater is also controlled by an Arduino.  Eventually I'll have individual Arduino's controlling each of the ceiling-fans/lights. I'm also building an EVSE for charging the EVs that can tell them to only use as much current as we can spare at the time

The dryer and oven will be manually controlled, i.e. don't use them when the battery bank is low.

I'm also modifying the dryer to pull air from the attic(above the insulation).  During the daytime that air is almost always hotter than the air in the house and during spring-fall it's often over 120F with very low humidity.  This should reduce the energy consumption on the dryer, I expect that for 3-4 months a year it won't even need to use the heating coils.

peter, would it be possible to post some links specifically about your power monitoring software and equipment. We use the ted gear  at work but I'd love to play with some arduino toys for it.
Thanks,  David

Hi David,

I'm working on some improvements to my data collection software, as soon as it's ready for prime time (hopefully by the end of the week) I'll start a new thread and post links to the software.
The software is designed to run on an Arm processor (like a Raspberry Pi) running linux and it's setup to collect data from an ECM-1240. However, the software is modular so that should make it easier to work with other monitoring systems,  I'm getting ready to add the ability to accept data from named pipes.

I just finished setting it up so it can be compiled to run as either a tradition forking daemon or the simplified systemd version, I'm just having problems getting it to log errors, etc. to the systemd journal.

I am slowly scaling up, as of now I have a 5 KWH Tesla battery module    I run my aquaponics setup and table saw with it.

My next plan is to buy an electric car and use the solar to charge it up / run the household.

EV TV on youtube Jack Richardson has hacked the Tesla Battery ( the entire thing ) so it can run off solar, and also power your home.